1. Field of the Invention
The present invention generally relates to communications over packet networks, such as Internet Protocol (“IP”) and, more particularly, to connecting communication devices over IP, such as connecting modem or facsimile devices over IP.
2. Related Art
Today the traditional analog telephony is being rapidly replaced with digital IP. telephony, which use various techniques to break voice into data packets for transmission over packet networks. Analog modems have been utilized to provide data, facsimile and voice communications over twisted pair telephone lines for decades. Modem is an analog-to-digital and digital-to-analog converter, which is capable of adapting a terminal or computer to an analog telephone line by converting digital pulses to audio frequencies and vice versa. Because a significant infrastructure is in place using such modems, the packet networks need to address and support modem communication.
FIG. 1 illustrates a block diagram of a conventional communications network 100 utilizing modems for communication over a packet network protocol, such as Internet Protocol, which may also be referred to as Modem over Internet Protocol (“MoIP”). As shown, communications network 100 includes first communication device 102 in communication with first gateway device 104 and second gateway device 114 in communication with second communication device 122. Communications network 100 further includes a packet network protocol, such as IP 112 to provide communications between first gateway device 104 and second gateway device 114. IP 112 implements the network layer (layer 3) of a network protocol, which contains a network address and is used to route a message to a different network or subnetwork. IP 112 accepts packets from the layer 4 transport protocol, such as Transmission Control Protocol (“TCP”) or User Data Protocol (“UDP”), and adds its own header and delivers the data to the layer 2 data link protocol. TCP provides transport functions, which ensures that the total amount of bytes sent is received correctly at the other end. UDP, which is part of the TCP/IP suite, is an alternate transport that does not guarantee delivery. UDP is widely used for real-time voice and video transmissions where erroneous packets are not retransmitted.
Devices 102, 104, 114 and 122 may include modems (modulator-demodulator). Modems may support a variety of data modulation standards, such as ITU (International Telecommunications Union) standards: V.22bis, V.34, V.90 or V.92, etc. Devices 102, 104, 114 and 122 may also include cable or DSL modems, which are all digital and technically not modems, but referred to as modems in the industry. Typically, modems have built-in error correction, such as MNP2-4 or LAPM (or V.42) and data compression, such as MNP5, V.42bis or V.44. Modems are also capable of supporting various voice and facsimile standards.
The communication process begins when first communication device 102, e.g. first modem (“M1”), originates a call to establish communications with second communication device 122, e.g. second modem (“M2”). First gateway device 104 (“G1”) receives the call and informs second gateway device 114 (“G2”) of the call for M2 over communications network 100 and, as a result, G2 calls M2.
Typically, in the default mode of operation, G1 and G2 communicate in voice mode and use compressed voice protocol, such as the ITU standard G.723. After M2 receives the call from G2, M2 answers the call and starts sending an answer tone, which is typically transmitted at about 2100 Hz frequency. At this point, G2 starts confirming the answer tone for a pre-defined period of time, e.g. 300 ms to 1000 ms. Once G2 confirms the answer tone, G2 informs G1 that the present communication session is a modem or facsimile session.
However, once G2 detects the answer tone, e.g., 2100 Hz tone, from M2, then G2 and G1 switch to an uncompressed voice protocol, such as an ITU standard G.711, which provides toll quality audio at 64 Kbps using either A-Law or mu-Law pulse code modulation methods. This uncompressed digital format is used in order to allow easy connections to legacy telephone networks. By switching to G.711, the signals generated by M2 may propagate through from G2 to G1 in a more intact manner in order to reach the first modem at the other side. Alternatively, once G2 detects the answer tone from M2, then G1 and G2 may switch into other modes designed to accommodate modem or facsimile devices.
However, there are many drawbacks in the above-described method and system of connecting communication devices, such as modems and facsimile devices over IP. As described above, G2 must confirm presence of answer tone for a sufficient period of time prior to switching out of compressed voice mode, e.g. G.729 or G.723 to uncompressed voice mode, such as G.711, or to modem or facsimile mode, since a false detection of answer tone and thus, a false switch by G1 and G2 to modem or facsimile mode would cause an undesirable interruption in voice communications. For example, noise or a female voice may be misinterpreted as a modem answer tone if answer tone is not properly confirmed and voice communication would be interrupted by switching G1 and G2 to modem or facsimile mode.
One specific problem occurs when M1 receives M2's answer tone while G2 is confirming M2's answer tone to determine whether to switch to modem or facsimile mode. It should be noted that while G2 is confirming M2's answer tone, G2 and G1 are in voice mode communication, and therefore, M1 can receive M2's answer tone while G2 is confirming the presence of an answer tone. The problem occurs when M1 starts acting on M2's answer tone, for example, M1 detects and confirms the answer tone and starts responding to M2's answer tone prior to G2 and G1 switching to modem or facsimile mode. Further, M1 and M2 may go into a handshaking process, which may be difficult to stop and re-start once it begins.
One possible solution may be for G2 to block any incoming signal coming from M2 122 for a pre-determined amount of time, e.g. five to ten seconds, after G2 114 places a call to M2 122. Modem answer tones, in general, last about three to four seconds and are generated by M2 122 upon answering the call. If the answer tone is blocked, then M1 102 will continue to wait until G1 and G2 switch over to properly handle a modem communication.
However, such solution may be unsuitable for voice calls over IP. It should be noted, as explained above, the communications network 100 defaults to voice mode and has no knowledge that at second communication device 122 is a modem or a facsimile device. As such, communications network 100 cannot readily block the modem signals of communication device 122 exclusively. Thus, communications network 100 would need to block the first 5 or 10 seconds in all cases, voice, modem, or facsimile. Since such method blocks all signals for the first 5 or 10 seconds, it would also have to block voice signals. Blocking voice signals may be unacceptable for users.
Accordingly, there is an intense need in the art for communication networks utilizing a packet network protocol that are able to efficiently, reliably and timely detect and support modem communications, such as data and facsimile modems.